Riedel's thyroiditis in a patient with retroperitoneal fibrosis.

A 56-yr-old man was known with retroperitoneal fibrosis. Seven years later he developed a painful swelling of the left thyroid lobe, which turned out to be Riedel's thyroiditis. The associations between Riedel's thyroiditis, retroperitoneal fibrosis, mediastinal fibrosis, sclerosing cholangitis and fibrosis in other organ systems are thought to be manifestations of multifocal idiopathic fibrosclerosis.